Underwater sailing body and method of controlling posture of underwater sailing body

ABSTRACT

An underwater sailing body includes: a positioning device configured to detect positional information of a hull of the underwater sailing body; a posture detecting sensor configured to detect posture information of the hull; an actuator configured to apply thrust to the hull in a front-rear direction of the hull, a left-right direction of the hull, an upper-lower direction of the hull in water to change the position and posture of the hull; and a controller configured to control the actuator. In order to hold a hull at a target position when the hull receives an external force by disturbances, the hull keeps balance by using thrusters with respect to the external force acting on the hull. Specifically, the hull is held at the target position by controlling a thruster configured to generate thrust in a front-rear direction and a thruster configured to generate thrust in a left-right direction.

TECHNICAL FIELD

The present invention relates to an underwater sailing body and a methodof controlling a posture of the underwater sailing body.

BACKGROUND ART

To hold a hull at a target position when the hull receives an externalforce by disturbances, such as waves and ocean currents, the hull needsto keep balance by using thrusters with respect to the external forceacting on the hull. Specifically, the hull is held at the targetposition by controlling a thruster configured to generate thrust in afront-rear direction and a thruster configured to generate thrust in aleft-right direction.

However, in some cases, the hull cannot receive electric power supply atsea. Therefore, it is desired to suppress the amount of electric powerconsumed, for example, when the thrusters are driven to hold the hull atthe target position. For example, proposed as a technique of holding ahull at a target position while suppressing electric power consumptionis an automatic direction setting method in which: a bow of a ship isdirected in a direction of a resultant force of disturbances(hereinafter referred to as a “direction in which an external forceacts”); and the ship is held at a target position (PTL 1). According tothe automatic direction setting method of PTL 1, the electric powerconsumption necessary to hold the hull at the target position can besuppressed by directing the bow in the direction in which the externalforce acts.

CITATION LIST Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 2000-302098

SUMMARY OF INVENTION Technical Problem

According to the automatic direction setting method of PTL 1, whenholding the hull at the target position, the electric power consumptioncan be suppressed by directing the bow in the direction in which theexternal force acts. However, although the automatic direction settingmethod of PTL 1 considers the control of the position and posture of theship on a horizontal plane, it does not consider a case where as in anunderwater sailing body, such as an AUV (autonomous underwater vehicle),the external force is applied to the hull not only in a left-rightdirection but also in an upper-lower direction.

The present invention was made to solve the above problem, and an objectof the present invention is to provide an underwater sailing body and amethod of controlling a posture of the underwater sailing body, each ofwhich can hold a hull at a target position while suppressing electricpower consumption.

Solution to Problem

An underwater sailing body according to an aspect of the presentinvention includes: a positioning device configured to detect positionalinformation indicating a position of a hull of the underwater sailingbody; a posture detecting sensor configured to detect postureinformation indicating a posture of the hull; an actuator configured toapply thrust to the hull in a front-rear direction of the hull, aleft-right direction of the hull, and an upper-lower direction of thehull in water to change the position and posture of the hull; and acontroller configured to control the actuator, wherein: in order to holdthe hull at a target position based on the positional informationdetected by the positioning device, the controller calculates acontrolling force in the front-rear direction of the hull, a controllingforce in the left-right direction of the hull, a controlling force inthe upper-lower direction of the hull, a turn controlling force ofturning the hull in a roll direction of the hull, a turn controllingforce of turning the hull in a yaw direction of the hull, and a turncontrolling force of turning the hull in a pitch direction of the hull,and controls the actuator based on the calculated forces; and when anexternal force is applied to the hull held at the target position, thecontroller updates target posture information such that each of thecontrolling force in the left-right direction and the controlling forcein the upper-lower direction becomes zero, and controls the actuatorsuch that the posture of the hull is changed to a posture correspondingto the updated posture information based on the posture informationdetected by the posture detecting sensor.

The front-rear direction denotes a direction from a stern of the hull toa bow of the hull or from the bow to the stern. The left-right directiondenotes a direction from port of the hull to starboard of the hull orfrom the starboard to the port. The upper-lower direction denotes adirection from a bottom surface of the hull to an upper surface of thehull or from the upper surface to the bottom surface.

According to the above configuration, when the external force is appliedto the hull held at the target position, the controller can change theposture of the hull by controlling the actuator such that each of thecontrolling force in the left-right direction and the controlling forcein the upper-lower direction becomes zero. The posture by which each ofthe controlling force in the left-right direction and the controllingforce in the upper-lower direction becomes zero denotes the posture inwhich the bow is directed in the direction in which the external forceacts. Typically, the hull is designed such that fluid resistance becomeslow when the hull advances. Therefore, the posture in which the bow isdirected in the direction in which the external force acts denotes theposture by which a fluid force acting on the hull is reduced.

As above, even when the external force is applied to the hull, theunderwater sailing body can take the posture by which the fluid forceacting on the hull is reduced. Therefore, the amount of electric powerconsumed by the actuator driven to hold the hull at the target positioncan be reduced.

Thus, the underwater sailing body according to the above aspect of thepresent invention has an effect of being able to hold the hull at thetarget position while suppressing the electric power consumption.

The underwater sailing body according to another aspect of the presentinvention may be configured such that: the controller includes acontrolling force calculating portion configured to calculate thecontrolling force in the front-rear direction, the controlling force inthe left-right direction, the controlling force in the upper-lowerdirection, the turn controlling force in the roll direction, the turncontrolling force in the yaw direction, and the turn controlling forcein the pitch direction from a difference between target positionalinformation and the positional information detected by the positioningdevice and a difference between the target posture information and theposture information detected by the posture detecting sensor; and whenthe external force is applied to the hull held at the target position,the controller updates a command value of a yaw angle of the targetposture information and a command value of a pitch angle of the targetposture information such that each of the controlling force in theleft-right direction and the controlling force in the upper-lowerdirection, which are calculated by the controlling force calculatingportion, becomes zero.

According to the above configuration, the controller can update thecommand value of the yaw angle and the command value of the pitch angle.Therefore, even when the external force is applied to the hull, the hullcan turn in the yaw direction and the pitch direction to take theposture by which each of the controlling force in the left-rightdirection and the controlling force in the upper-lower direction becomeszero, i.e., the posture by which the fluid force acting on the hull isreduced.

The underwater sailing body according to yet another aspect of thepresent invention may further include a flow direction meter configuredto measure a tidal current incoming direction that is a direction of theexternal force applied to the hull, wherein the controller may updatethe command value of the yaw angle and the command value of the pitchangle based on the target posture information indicating the posture ofthe hull in which the bow is directed in the tidal current incomingdirection measured by the flow direction meter.

According to the above configuration, since the flow direction meter isincluded, the tidal current incoming direction, i.e., the direction ofthe external force applied to the hull can be recognized. Therefore,based on the measurement result of the flow direction meter, thecontroller can recognize the posture by which each of the controllingforce in the left-right direction and the controlling force in theupper-lower direction becomes zero, i.e., the posture by which the fluidforce acting on the hull is reduced, and can update the command value ofthe yaw angle and the command value of the pitch angle such that thehull takes the above posture.

The underwater sailing body according to still another aspect of thepresent invention may be configured such that: the controller includes afirst change rate limiter configured to limit a change amount of theturn controlling force in the pitch direction, the change amount beingcalculated from a difference between the updated command value of thepitch angle and a value of the pitch angle of the posture informationdetected by the posture detecting sensor and a second change ratelimiter configured to limit a change amount of the turn controllingforce in the yaw direction, the change amount being calculated from adifference between the updated command value of the yaw angle and avalue of the yaw angle of the posture information detected by theposture detecting sensor; and the controller changes setting of thechange amount of the first change rate limiter and setting of the changeamount of the second change rate limiter and updates the command valueof the yaw angle and the command value of the pitch angle in this order,or the controller sets a speed of updating the command value of thepitch angle to be lower than a speed of updating the command value ofthe yaw angle.

According to the above configuration, since the controller includes thefirst change rate limiter and the second change rate limiter, it ispossible to prevent a case where: the change amount of the turncontrolling force in the pitch direction and the change amount of theturn controlling force in the yaw direction become large; the hulllargely turns in the pitch direction and the yaw direction todrastically change the posture.

Further, the controller can change the setting of the first change ratelimiter and the setting of the second change rate limiter and update thecommand value of the yaw angle and the command value of the pitch anglein this order. Or, the controller can set the speed of updating thecommand value of the yaw angle to be higher than the speed of updatingthe command value of the pitch angle. Therefore, the turn in the yawdirection can be performed preferentially over the turn in the pitchdirection. On this account, it is possible to prevent a case where, forexample, when the hull changes the posture to deal with the externalforce applied from a rear and diagonally-upper side of the hull, thepitch angle exceeds 90°, and the hull takes an abnormal posture in whichthe upper surface and bottom surface of the hull are reversed.

The underwater sailing body according to yet another aspect of thepresent invention may be configured such that: the controller includes ayaw angle command value calculating portion configured to integrate avalue of the controlling force in the left-right direction to calculatea target command value of the yaw angle and a pitch angle command valuecalculating portion configured to integrate a value of the controllingforce in the upper-lower direction to calculate a target command valueof the pitch angle; and until each of the controlling force in theleft-right direction and the controlling force in the upper-lowerdirection becomes zero, the controller updates the command value of theyaw angle and the command value of the pitch angle by the command valuecalculated by the yaw angle command value calculating portion and thecommand value calculated by the pitch angle command value calculatingportion.

According to the above configuration, since the controller includes theyaw angle command value calculating portion and the pitch angle commandvalue calculating portion, the controller can update the command valueof the yaw angle and the command value of the pitch angle to change theposture of the hull to the posture by which each of the controllingforce in the left-right direction and the controlling force in theupper-lower direction becomes zero.

Therefore, even when the controller does not include the flow directionmeter, the controller can change the posture of the hull to the postureby which each of the controlling force in the left-right direction andthe controlling force in the upper-lower direction becomes zero, i.e.,the posture by which the fluid force acting on the hull is reduced.

The underwater sailing body according to still another aspect of thepresent invention may be configured such that: the yaw angle commandvalue calculating portion calculates the target command value of the yawangle from a value obtained by integrating a value obtained bymultiplying the value of the controlling force in the left-rightdirection by a gain; the pitch angle command value calculating portioncalculates the target command value of the pitch angle from a valueobtained by integrating a value obtained by multiplying the value of thecontrolling force in the upper-lower direction by a gain; and thecontroller changes a value of the gain by which the yaw angle commandvalue calculating portion multiplies the value of the controlling forcein the left-right direction and a value of the gain by which the pitchangle command value calculating portion multiplies the value of thecontrolling force in the upper-lower direction, and updates the commandvalue of the yaw angle and the command value of the pitch angle in thisorder, or the controller sets a speed of updating the command value ofthe pitch angle to be lower than a speed of updating the command valueof the yaw angle.

According to the above configuration, the yaw angle command valuecalculating portion calculates the target command value of the yaw anglefrom the value obtained by integrating the value obtained by multiplyingthe value of the controlling force in the left-right direction by thegain, and the pitch angle command value calculating portion calculatesthe target command value of the pitch angle from the value obtained byintegrating the value obtained by multiplying the value of thecontrolling force in the upper-lower direction by the gain. Therefore,the controller can change the settings of the values of the above gainsand update the command value of the yaw angle and the command value ofthe pitch angle in this order. Or, the controller can set the speed ofupdating the command value of the yaw angle to be higher than the speedof updating the command value of the pitch angle.

Therefore, the turn in the yaw direction can be performed preferentiallyover the turn in the pitch direction. On this account, it is possible toprevent a case where, for example, when the hull changes the posture todeal with the external force applied from a rear and diagonally-upperside of the hull, the pitch angle exceeds 90°, and the hull takes theabnormal posture in which the upper surface and bottom surface of thehull are reversed.

The underwater sailing body according to yet another aspect of thepresent invention may be configured such that the actuator includes agravity center position changing portion configured to move in thefront-rear direction in the hull so as to change a gravity centerposition of the hull.

According to above configuration, since the gravity center positionchanging portion is included, the gravity center position of the hullcan be changed in the front-rear direction. Therefore, a rotationaldirection of pitching of the hull can be easily determined, andtherefore, the control of the turn in the pitch direction can befacilitated.

A method of controlling a posture of an underwater sailing bodyaccording to an aspect of the present invention is a method ofcontrolling a posture of an underwater sailing body, the underwatersailing body including: a positioning device configured to detectpositional information indicating a position of a hull of the underwatersailing body; a posture detecting sensor configured to detect postureinformation indicating a posture of the hull; an actuator configured toapply thrust to the hull in a front-rear direction of the hull, aleft-right direction of the hull, and an upper-lower direction of thehull in water to change the position and posture of the hull; and acontroller configured to control the actuator, the method including: inorder to hold the hull at a target position based on the positionalinformation detected by the positioning device, calculating by thecontroller a controlling force in the front-rear direction of the hull,a controlling force in the left-right direction of the hull, acontrolling force in the upper-lower direction of the hull, a turncontrolling force of turning the hull in a roll direction of the hull, aturn controlling force of turning the hull in a yaw direction of thehull, and a turn controlling force of turning the hull in a pitchdirection of the hull, and controlling the actuator by the controllerbased on the calculated forces; and when an external force is applied tothe hull held at the target position, updating, by the controller,target posture information such that each of the controlling force inthe left-right direction and the controlling force in the upper-lowerdirection becomes zero, and controlling the actuator by the controllersuch that the posture of the hull is changed to a posture correspondingto the updated posture information based on the posture informationdetected by the posture detecting sensor.

According to the above method, when the external force is applied to thehull held at the target position, the controller can control theactuator to change the posture of the hull such that each of thecontrolling force in the left-right direction and the controlling forcein the upper-lower direction becomes zero. The posture by which each ofthe controlling force in the left-right direction and the controllingforce in the upper-lower direction becomes zero denotes the posture inwhich the bow is directed in the direction in which the external forceacts, i.e., the posture by which the fluid force acting on the hull isreduced.

As above, even when the external force is applied to the hull, the hullcan take the posture by which the fluid force acting on the hull isreduced. Therefore, the amount of electric power consumed by theactuator driven to hold the hull at the target position can be reduced.

Therefore, the method of controlling the posture of the underwatersailing body according to the aspect of the present invention has aneffect of being able to hold the hull at the target position whilesuppressing the electric power consumption.

Advantageous Effects of Invention

The present invention is configured as explained above, and each of theunderwater sailing body according to the present invention and themethod of controlling the posture of the underwater sailing bodyaccording to the present invention has the effect of being able to holdthe hull at the target position while suppressing the electric powerconsumption.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are diagrams each showing one example of actuatorsincluded in an underwater sailing body according to Embodiment 1 of thepresent invention. FIG. 1A is a top view (plan view) of the underwatersailing body. FIG. 1B is a side view of the underwater sailing body.

FIG. 2 is a block diagram showing one example of components related to atarget position holding operation of the underwater sailing bodyaccording to Embodiment 1 of the present invention.

FIGS. 3A and 3B are diagrams each showing one example of a posture ofthe underwater sailing body of FIG. 2 on a horizontal plane. FIG. 3Ashows one example of the posture of the underwater sailing body whendisturbances occur. FIG. 3B shows one example of the posture of theunderwater sailing body which posture is changed in accordance with theoccurrence of the disturbances.

FIGS. 4A and 4B are diagrams each showing one example of the posture ofthe underwater sailing body of FIG. 2 in a vertical direction. FIG. 4Ashows one example of the posture of the underwater sailing body whendisturbances occur. FIG. 4B shows one example of the posture of theunderwater sailing body which posture is changed in accordance with theoccurrence of the disturbances.

FIG. 5 is a block diagram showing components related to the control ofthe posture of the underwater sailing body of Embodiment 1 whendisturbances occur.

FIG. 6 is a diagram showing one example showing a state where thedirection of a bow of the underwater sailing body of Embodiment 1changes from a front and upper direction to a rear and upper direction.

FIG. 7 is a block diagram showing components related to the control ofthe posture of the underwater sailing body of Embodiment 2 whendisturbances occur.

FIG. 8 is a diagram schematically showing one example of theconfiguration of a modified example of the underwater sailing body.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be explained withreference to the drawings. The present description explains an examplein which an underwater sailing body 1 according to the present inventionis a submersible vessel, such as an AUV. However, the underwater sailingbody 1 of the present invention is not limited to this and is onlyrequired to be an underwater sailing body that is held at a targetposition in water and performs work, for example.

Embodiment 1

FIGS. 1A and 1B are diagrams each showing one example of actuators 3included in the underwater sailing body 1 according to Embodiment 1 ofthe present invention. FIG. 1A is a top view (plan view) of theunderwater sailing body 1, and FIG. 1B is a side view of the underwatersailing body 1. For convenience of explanation, FIG. 1 shows only thearrangement of the actuators 3 included in the underwater sailing body1.

As shown in FIGS. 1A and 1B, the underwater sailing body 1 has asubstantially rectangular solid shape formed such that an area of eachof upper and lower surfaces of a hull 2 is larger than an area of eachof left, right, front, and rear side surfaces of the hull 2. As theactuators 3, the underwater sailing body 1 includes: two main propulsionunits 31 a and 31 b configured to move the hull 2 in a front-reardirection; four vertical thrusters 32 a, 32 b, 32 c, and 32 d configuredto move the hull 2 in an upper-lower direction; and two horizontalthrusters 33 a and 33 b configured to move the hull 2 in a left-rightdirection. It should be noted that: each of the main propulsion units 31a and 31 b is simply referred to as a main propulsion unit 31 when it isunnecessary to distinguish between the main propulsion units 31 a and 31b; each of the vertical thrusters 32 a, 32 b, 32 c, and 32 d is simplyreferred to as a vertical thruster 32 when it is unnecessary todistinguish among the vertical thrusters 32 a, 32 b, 32 c, and 32 d; andeach of the horizontal thrusters 33 a and 33 b is referred to as ahorizontal thruster 33 when it is unnecessary to distinguish between thehorizontal thrusters 33 a and 33 b.

As shown in FIG. 1A, in the underwater sailing body 1 of Embodiment 1,the two main propulsion units 31 a and 31 b are provided such thatrotating shafts of propellers of the main propulsion units 31 a and 31 bextend along an axis extending in the front-rear direction of the hull2. Further, the two horizontal thrusters 33 a and 33 b are provided suchthat rotating shafts of propellers of the horizontal thrusters 33 a and33 b extend along an axis extending in the left-right direction of thehull 2. Furthermore, the four vertical thrusters 32 a, 32 b, 32 c, and32 d are provided such that rotating shafts of propellers of thevertical thrusters 32 a, 32 b, 32 c, and 32 d extend along an axisextending in the upper-lower direction of the hull 2.

The underwater sailing body 1 can move the hull 2 in the front-reardirection by the two main propulsion units 31 a and 31 b and can alsomove the hull 2 in the left-right direction by the two horizontalthrusters 33 a and 33 b. The underwater sailing body 1 can control arotational movement of the hull 2 in a yaw direction by adjustingoutputs of the two horizontal thrusters 33 a and 33 b. Further, theunderwater sailing body 1 can move the hull 2 in the upper-lowerdirection by the four vertical thrusters 32 a, 32 b, 32 c, and 32 d. Theunderwater sailing body 1 can control a rotational movement of the hull2 in a pitch direction and a rotational movement of the hull 2 in a rolldirection by adjusting outputs of the four vertical thrusters 32 a, 32b, 32 c, and 32 d.

As shown in FIGS. 1A and 1B, the hull 2 of the underwater sailing body 1has a substantially rectangular solid shape. However, the presentembodiment is not limited to this, and the shape of the hull 2 issuitably selected depending on, for example, a purpose of work performedby the underwater sailing body 1. As described above, as the actuators3, the underwater sailing body 1 of Embodiment 1 includes the two mainpropulsion units 31 a and 31 b, the four vertical thrusters 32 a, 32 b,32 c, and 32 d, and the two horizontal thrusters 33 a and 33 b. However,the number of actuators 3 and the types of the actuators 3 are notlimited to these.

For example, the underwater sailing body 1 may be configured such that:the rotating shafts of the propellers of the two main propulsion units31 a and 31 b are provided so as to be inclined at an angle of about 45°with respect to a center line (not shown) extending in the front-reardirection of the underwater sailing body 1 and so as to extend to aleft-rear side and a right-rear side, respectively; and the movements ofthe hull 2 in the front-rear direction and the left-right direction andthe rotational movement of the hull 2 in the yaw direction arecontrolled by the main propulsion units 31 a and 31 b.

To be specific, the underwater sailing body 1 is only required to beconfigured such that: the hull 2 can move in the front-rear direction,the left-right direction, and the upper-lower direction; and the postureof the hull 2 can be changed by rotating the hull 2 in the rolldirection, the yaw direction, and the pitch direction. Therefore, thenumber of actuators 3 and the types of the actuators 3 may be determinedarbitrarily.

Components and Control Flow for Holding Hull at Target Position

Next, components for holding the hull 2 at a target position by usingthe actuators 3 will be explained with reference to FIG. 2. FIG. 2 is ablock diagram showing one example of components related to a targetposition holding operation of the underwater sailing body 1 according toEmbodiment 1 of the present invention. For convenience of explanation,in FIG. 2, flows of command values of x, y, and z coordinatescorresponding to positional information indicating the position of thehull 2 are collectively shown by one arrow. Further, flows of commandvalues of a roll angle, a pitch angle, and a yaw angle corresponding toposture information indicating the posture of the hull 2 arecollectively shown by one arrow.

As shown in FIG. 2, the underwater sailing body 1 includes a gyro sensor8, a positioning device 9, and a controller 50 in addition to theactuators 3.

The gyro sensor 8 is one example of a posture detecting sensor of thepresent invention and detects the posture information indicating theposture of the hull 2. The positioning device 9 detects the positionalinformation indicating the position of the hull 2. It should be notedthat a publicly known acoustic positioning device configured to useultrasound to measure a relative position of the hull 2 from a mothership or a predetermined position on the seabed as a reference point canbe utilized as the positioning device 9.

The controller 50 performs various control operations of the underwatersailing body 1 and includes a first comparing portion 4, a secondcomparing portion 5, a controlling force calculating portion 6, and athrust distributing device 7. The first comparing portion 4 calculates adifference between the command value of the x coordinate as a targetvalue and the command value of the measured x coordinate, a differencebetween the command value of the y coordinate as a target value and thecommand value of the measured y coordinate, and a difference between thecommand value of the z coordinate as a target value and the commandvalue of the measured z coordinate. It should be noted that theunderwater sailing body 1 includes first comparing portions 4 a, 4 b,and 4 c for the respective command values of the x, y, and z coordinates(see FIG. 7 described below). However, each of the first comparingportions 4 a, 4 b, and 4 c is referred to as the first comparing portion4 when it is unnecessary to distinguish among the first comparingportions 4 a, 4 b, and 4 c. Further, the second comparing portion 5calculates a difference between the command value of the roll angle as atarget value and the command value of the measured roll angle, adifference between the command value of the pitch angle as a targetvalue and the command value of the measured pitch angle, and adifference between the command value of the yaw angle as a target valueand the command value of the measured yaw angle. It should be noted thatthe underwater sailing body 1 includes second comparing portions 5 a, 5b, and 5 c for the roll angle, the pitch angle, and the yaw angle,respectively (see FIG. 7 described below). However, each of the secondcomparing portions 5 a, 5 b, and 5 c is simply referred to as the secondcomparing portion 5 when it is unnecessary to distinguish among thesecond comparing portions 5 a, 5 b, and 5 c.

From a difference between the target position at which the hull 2 isheld and the actual position of the hull 2 and a difference between thetarget posture of the hull 2 and the actual posture of the hull 2, thecontrolling force calculating portion 6 calculates: a front-rearcontrolling force that is a controlling force in the front-reardirection in the underwater sailing body 1; a left-right controllingforce that is a controlling force in the left-right direction in theunderwater sailing body 1; an upper-lower controlling force that is acontrolling force in the upper-lower direction in the underwater sailingbody 1; a roll turn controlling force that is a turn controlling forcein the roll direction in the underwater sailing body 1; a pitch turncontrolling force that is a turn controlling force in the pitchdirection in the underwater sailing body 1; and a yaw turn controllingforce that is a turn controlling force in the yaw direction in theunderwater sailing body 1.

Based on the calculation results of the controlling force calculatingportion 6, the thrust distributing device 7 calculates the thrustdistributed to the respective actuators 3. Then, the thrust distributingdevice 7 calculates operation amounts of the actuators 3 from thecalculated thrust and outputs the command values corresponding to thecalculated operation amounts to the actuators 3. More specifically, thethrust distributing device 7 calculates the pitch angles, the rotationalfrequencies, and the like of the propellers (not shown) of the mainpropulsion units 31, the horizontal thrusters 33, and the verticalthrusters 32 constituting the actuators 3 and outputs the command valuesof the pitch angles, the rotational frequencies, and the like.

According to the underwater sailing body 1 configured as above, the hull2 can be held at the target position by the following control flow. Tobe specific, first, a ship operator inputs as the target values to theunderwater sailing body 1 (i) the command values indicating the positionat which the hull 2 is held, by values of x-, y-, and z-axes of an earthfixed coordinate system and (ii) the command values of the roll angle,the pitch angle, and the yaw angle which define the posture of theunderwater sailing body 1. The first comparing portion 4 calculates thedifference between the value of the x-axis indicating the actualposition of the hull 2 and obtained from the positioning device 9 andthe value of the x-axis as the target value, the difference between thevalue of the y-axis indicating the actual position of the hull 2 andobtained from the positioning device 9 and the value of the y-axis asthe target value, and the difference between the value of the z-axisindicating the actual position of the hull 2 and obtained from thepositioning device 9 and the value of the z-axis as the target value,and inputs the differences to the controlling force calculating portion6. Further, the second comparing portion 5 calculates the differencebetween the roll angle indicating the actual posture of the hull 2 andobtained from the gyro sensor 8 and the value of the roll angle as thetarget value, the difference between the pitch angle indicating theactual posture of the hull 2 and obtained from the gyro sensor 8 and thevalue of the pitch angle as the target value, and the difference betweenthe yaw angle indicating the actual posture of the hull 2 and obtainedfrom the gyro sensor 8 and the value of the yaw angle as the targetvalue, and inputs the differences to the controlling force calculatingportion 6.

The controlling force calculating portion 6 calculates the front-rearcontrolling force, the left-right controlling force, the upper-lowercontrolling force, the roll turn controlling force, the pitch turncontrolling force, and the yaw turn controlling force in the underwatersailing body 1, calculates the command values from the calculationresults, and inputs the command values to the thrust distributing device7. The thrust distributing device 7 calculates the thrust distributed tothe respective actuators 3 from the input command values. The thrustdistributing device 7 calculates the operation amounts of the actuators3 from the calculated thrust and outputs the command values indicatingthe operation amounts to the actuators 3. By executing the above controlflow, the underwater sailing body 1 of Embodiment 1 can hold the hull 2at the target position.

The underwater sailing body 1 of Embodiment 1 is configured such thatwhen disturbances occur in a state where the hull 2 is held at thetarget position, to suppress the electric power consumption, the hull 2takes a posture in which a bow of the hull 2 is directed in thedirection of an external force generated by the disturbances, i.e., aposture by which a fluid force acting on the hull 2 is reduced. Forexample, when the external force is applied to the hull 2 from aleft-front and diagonally-upper side of the hull 2 as shown in FIGS. 3A,3B, 4A, and 4B, the front-rear controlling force is applied to the hull2 in the front direction, the left-right controlling force is applied tothe hull 2 in the left direction, and the upper-lower controlling forceis applied to the hull 2 in the upper direction. Thus, the hull 2 keepsbalance so as to be held at the target position. The bow of theunderwater sailing body 1 is directed in the direction in which theexternal force acts, and the underwater sailing body 1 takes a postureby which each of the left-right controlling force and the upper-lowercontrolling force becomes zero, in other words, the posture by which thefluid force acting on the hull is reduced.

FIGS. 3A and 3B are diagrams each showing one example of the posture ofthe underwater sailing body 1 of FIG. 2 on a horizontal plane. FIG. 3Ashows one example of the posture of the underwater sailing body 1 whendisturbances occur. FIG. 3B shows one example of the posture of theunderwater sailing body 1 which posture is changed in accordance withthe occurrence of the disturbances. FIGS. 4A and 4B are diagrams eachshowing one example of the posture of the underwater sailing body 1 ofFIG. 2 in a vertical direction. FIG. 4A shows one example of the postureof the underwater sailing body 1 when disturbances occur. FIG. 4B showsone example of the posture of the underwater sailing body 1 whichposture is changed in accordance with the occurrence of thedisturbances.

Control of Posture by Utilizing Measurement Result of Flow DirectionMeter

Hereinafter, the control of the posture of the hull 2 of the underwatersailing body 1 of Embodiment 1 when disturbances occur will be explainedwith reference to FIG. 5. FIG. 5 is a block diagram showing componentsrelated to the control of the posture of the underwater sailing body 1of Embodiment 1 when disturbances occur. In FIG. 5, to more specificallyexplain the control of the posture of the hull 2, the flows of thecommand values of the roll angle, the pitch angle, and the yaw angle areshown by separate arrows.

As shown in FIG. 5, as the components related to the control of theposture of the hull 2 when disturbances occur, the underwater sailingbody 1 of Embodiment 1 includes a flow direction meter 11, and thecontroller 50 further includes a first change rate limiter 12 and asecond change rate limiter 13.

The flow direction meter 11 is a device configured to measure a tidalcurrent incoming direction. For example, each of the first change ratelimiter 12 and the second change rate limiter 13 limits a change amountper second of the calculated command value. In the underwater sailingbody 1, the first change rate limiter 12 limits the change amount persecond of the command value of the pitch angle, and the second changerate limiter 13 limits the change amount per second of the command valueof the yaw angle.

As described above, according to the underwater sailing body 1, thecontrolling force calculating portion 6 calculates the front-rearcontrolling force, the left-right controlling force, the upper-lowercontrolling force, the roll turn controlling force, the pitch turncontrolling force, and the yaw turn controlling force in the underwatersailing body 1 based on the difference between the command value (x_(t))of the x coordinate as the target value and the command value (x) of thex coordinate indicating the measured position of the hull 2, thedifference between the command value (y_(t)) of the y coordinate as thetarget value and the command value (y) of the y coordinate indicatingthe measured position of the hull 2, the difference between the commandvalue (z_(t)) of the z coordinate as the target value and the commandvalue (z) of the z coordinate indicating the measured position of thehull 2, the difference between the command value (φ_(r)) of the rollangle as the target value and the command value (φ) of the roll angleindicating the measured posture of the hull 2, the difference betweenthe command value (θ_(t)) of the pitch angle as the target value and thecommand value (θ) of the pitch angle indicating the measured posture ofthe hull 2, and the difference between the command value (Ψ_(t)) of theyaw angle as the target value and the command value (Ψ) of the yaw angleindicating the measured posture of the hull 2. The thrust distributingdevice 7 calculates the thrust distributed to the respective actuators 3based on the calculation results of the controlling force calculatingportion 6, calculates the operation amounts of the actuators 3 from thecalculated thrust, and controls the actuators 3 based on the operationamounts of the actuators 3 to hold the hull 2 at the target position.

According to this configuration, when the external force is applied tothe hull 2, the underwater sailing body 1 turns only in the pitchdirection and the yaw direction with respect to the external force tochange the posture thereof. Therefore, only the command value of thepitch angle and the command value of the yaw angle are updated by usinginformation indicating the tidal current direction obtained from theflow direction meter 11. Hereinafter, the update of the command value ofthe pitch angle and the update of the command value of the yaw anglewill be explained.

According to the underwater sailing body 1, first, the direction inwhich the external force acts (tidal current incoming direction) ismeasured by the flow direction meter 11. The command value (θ_(t)) ofthe pitch angle as the target value is updated to the value (θ_(c)) ofthe pitch angle of the posture in which the bow is directed in the tidalcurrent incoming direction measured by the flow direction meter 11, andthe command value (Ψ_(t)) of the yaw angle as the target value isupdated to the value (Ψ_(c)) of the yaw angle of the posture in whichthe bow is directed in the tidal current incoming direction measured bythe flow direction meter 11. The second comparing portion 5 b calculatesa difference (θ_(c)−θ) between the updated value (θ_(c)) of the pitchangle and the command value θ of the pitch angle measured by the gyrosensor 8, and the second comparing portion 5 c calculates a difference(Ψ_(c)−Ψ) between the updated value (Ψ_(c)) of the yaw angle and thecommand value Ψ of the yaw angle measured by the gyro sensor 8. Thefirst change rate limiter 12 applies a change rate limit to thedifference regarding the command value of the pitch angle calculated bythe second comparing portion 5 b and inputs the obtained value to thecontrolling force calculating portion 6. Similarly, the second changerate limiter 13 applies a change rate limit to the difference regardingthe command value of the yaw angle calculated by the second comparingportion 5 c and inputs the obtained value to the controlling forcecalculating portion 6.

To prevent the posture of the hull 2 from being drastically changed whendisturbances occur, the underwater sailing body 1 includes the firstchange rate limiter 12 and the second change rate limiter 13. However,these members are not necessarily required when, for example, theunderwater sailing body 1 is used under such an environment that thechange in the posture due to the occurrence of the disturbances issmall.

The controlling force calculating portion 6 calculates the pitch turncontrolling force from the input value obtained by applying the changerate limit to the difference regarding the command value of the pitchangle. Further, the controlling force calculating portion 6 calculatesthe yaw turn controlling force from the input value obtained by applyingthe change rate limit to the difference regarding the command value ofthe yaw angle. Then, the controlling force calculating portion 6calculates the command value of the pitch turn controlling force and thecommand value of the yaw turn controlling force from the abovecalculation results and inputs these command values to the thrustdistributing device 7.

Based on the input command values of the respective turn controllingforces, the thrust distributing device 7 calculates the operationamounts of the actuators 3 such that the hull 2 turns in the pitchdirection and the yaw direction. Then, the thrust distributing device 7outputs the command values corresponding to the calculated operationamounts to the actuators 3. The above control flow is performed untilthe bow is directed in the direction of the external force applied tothe hull 2. As above, the underwater sailing body 1 according toEmbodiment 1 can change the posture so as to gradually direct the bow inthe direction of the external force while being held at a predeterminedposition.

When the external force is applied to the hull 2 from a rear anddiagonally-upper side of the hull 2, as shown in FIG. 6, the hull 2 maymove from a state where the bow is directed to a front anddiagonally-upper side to a state where the pitch angle of the hull 2exceeds 90°, and the bow is directed to a rear side. FIG. 6 is a diagramshowing one example of a state where the direction of the bow of theunderwater sailing body 1 of Embodiment 1 changes from a front and upperdirection to a rear and upper direction. In FIG. 6, the horizontal planecorresponds to an x-y plane, and the vertical direction corresponds tothe z-axis direction.

In this case, the hull 2 of the underwater sailing body 1 takes anabnormal posture, i.e., is turned upside down, and this is notpreferable for the control of the underwater sailing body 1 andpredetermined work performed by the underwater sailing body 1. As shownin FIG. 6, when the bow turns by an angle of 2° in the pitch directionfrom the posture (for example, (pitch, yaw)=(89°, 0°)) in which the bowis directed in the front and upper direction, to be directed in the rearand upper direction, the posture after this turn is represented by“(pitch, yaw)=(89°, 180°).” As above, a problem may arise, in whichregarding an azimuth angle indicating the posture, the yawdiscontinuously changes from 0° to 180°, and this causes instability ofcontrol.

To prevent the posture of the hull 2 from changing as shown in FIG. 6,the underwater sailing body 1 may be configured such that the posture inthe yaw direction is preferentially changed, and the posture in thepitch direction is then changed.

Specifically, according to the underwater sailing body 1, when theexternal force is applied to the hull 2, first, the first change ratelimiter 12 sets the change amount in the pitch direction to zero, andthe turn is performed only in the yaw direction. After the turn in theyaw direction, the second change rate limiter 13 sets the change amountin the yaw direction to zero, and the first change rate limiter returnsthe change amount, which is zero, to the initial value. Then, the turnis performed in the pitch direction.

Or, to prevent the posture of the hull 2 from changing as shown in FIG.6, the underwater sailing body 1 according to Embodiment 1 may beconfigured such that a speed of updating the pitch angle to the targetvalue is lower than a speed of updating the yaw angle to the targetvalue. Specifically, in the underwater sailing body 1, change rates areset such that the change amount of the first change rate limiter 12 issmaller than the change amount of the second change rate limiter 13.

As above, the underwater sailing body 1 according to Embodiment 1 may beconfigured such that the turn of the hull 2 in the yaw direction isperformed preferentially over the turn of the hull 2 in the pitchdirection. Therefore, the hull 2 can be prevented from taking theabnormal posture, and the unstable control before and after the abnormalposture can be avoided.

Embodiment 2 Control of Posture Without Flow Direction Meter

The control of the posture of an underwater sailing body 10 ofEmbodiment 2 when disturbances occur will be explained with reference toFIG. 7. The underwater sailing body 10 does not include the flowdirection meter 11. FIG. 7 is a block diagram showing components relatedto the control of the posture of the underwater sailing body 10 ofEmbodiment 2 when disturbances occur. As shown in FIG. 7, the underwatersailing body 10 of Embodiment 2 is different from the underwater sailingbody 1 of Embodiment 1 in that: the underwater sailing body 10 ofEmbodiment 2 does not include the flow direction meter 11; and thecontroller 50 of Embodiment 2 does not include the first change ratelimiter 12 and the second change rate limiter 13 but includes a yawangle command value calculating portion 21 and a pitch angle commandvalue calculating portion 22. Other than the above, the underwatersailing body 10 of Embodiment 2 is the same in configuration as theunderwater sailing body 1 of Embodiment 1. Therefore, the same referencesigns are used for the same members, and a repetition of the sameexplanation is avoided.

Although details will be described later, the yaw angle command valuecalculating portion 21 calculates the yaw angle command value as thetarget value and includes an integrator configured to integrate thecommand value of the left-right controlling force output from thecontrolling force calculating portion 6. Further, the pitch anglecommand value calculating portion 22 calculates the pitch angle commandvalue as the target value and includes an integrator configured tointegrate the command value of the upper-lower controlling force outputfrom the controlling force calculating portion 6.

Since the flow direction meter 11 is not included, the underwatersailing body 10 cannot directly recognize the tidal current incomingdirection (direction in which the external force acts). Therefore, theunderwater sailing body 10 is configured such that: the command value ofthe yaw angle is calculated from the left-right controlling force thatacts to hold the hull 2 at the predetermined position when the externalforce is applied to the hull 2; and the command value of the pitch angleis calculated from the upper-lower controlling force that acts to holdthe hull 2 at the predetermined position when the external force isapplied to the hull 2.

For example, as shown in FIGS. 3A, 3B, 4A, and 4B, when the externalforce is applied to the hull 2 from a left-front and diagonally-upperside, the hull 2 is controlled so as to turn and stop at a positionwhere the direction of the external force and the bow face each other,in other words, as shown in FIGS. 3B and 4B, a position where theleft-right controlling force is zero, and the upper-lower controllingforce is zero. For example, when the external force is applied to a portside of the hull 2 as shown in FIG. 3A, the left-right controlling forceacts in the left direction to hold the hull 2 at the target position. Incontrast, when the external force is applied to a starboard side of thehull 2, the left-right controlling force acts in the right direction tohold the hull 2 at the target position. When the external force isapplied to an upper side of the hull 2 as shown in FIG. 4A, theupper-lower controlling force acts in the upper direction. In contrast,when the external force is applied to a lower side of the hull 2, theupper-lower controlling force acts in the lower direction. Therefore, aturning direction of the hull 2 is determined based on acting directionsof the left-right controlling force and the upper-lower controllingforce, and the command value of the pitch angle and the command value ofthe yaw angle are updated on the basis that the direction of the bow inthe posture in which each of the left-right controlling force and theupper-lower controlling force is zero is the direction in which theexternal force acts.

Specifically, by the following control flow, the underwater sailing body10 of Embodiment 2 controls the posture of the hull 2 held at the targetposition. First, as with the underwater sailing body 1 of Embodiment 1,according to the underwater sailing body 10, the controlling forcecalculating portion 6 calculates the front-rear controlling force, theleft-right controlling force, the upper-lower controlling force, theroll turn controlling force, the pitch turn controlling force, and theyaw turn controlling force in the underwater sailing body 10 based onthe difference between the command value (x_(t)) of the x coordinate asthe target value and the command value (x) of the x coordinateindicating the measured position of the hull 2, the difference betweenthe command value (y_(t)) of the y coordinate as the target value andthe command value (y) of the y coordinate indicating the measuredposition of the hull 2, the difference between the command value (z_(t))of the z coordinate as the target value and the command value (z) of thez coordinate indicating the measured position of the hull 2, thedifference between the command value (φ_(t)) of the roll angle as thetarget value and the command value (φ) of the roll angle indicating themeasured posture of the hull 2, the difference between the command value(θ_(t)) of the pitch angle as the target value and the command value (θ)of the pitch angle indicating the measured posture of the hull 2, andthe difference between the command value (Ψ_(r)) of the yaw angle as thetarget value and the command value (Ψ) of the yaw angle indicating themeasured posture of the hull 2. Then, the thrust distributing device 7calculates the thrust distributed to the respective actuators 3 based onthe calculation results of the controlling force calculating portion 6,calculates the operation amounts of the actuators 3 from the calculatedthrust, and controls the actuators 3 to hold the hull 2 at the targetposition. According to this configuration, when the external force isapplied to the hull 2, the underwater sailing body 10 of Embodiment 2changes the posture of the hull 2 in the following manner.

To be specific, according to the underwater sailing body 10, the commandvalue of the controlling force acting in the left-right direction tohold the hull 2 at the target position when disturbances occur is inputto the yaw angle command value calculating portion 21, and the commandvalue of the controlling force acting in the upper-lower direction tohold the hull 2 at the target position when disturbances occur is inputto the pitch angle command value calculating portion 22. The yaw anglecommand value calculating portion 21 calculates the yaw angle commandvalue Ψ_(t) from a value obtained by integrating a value obtained bymultiplying the input command value of the left-right controlling forceby a gain, and updates the yaw angle command value Ψ_(t) as the targetvalue to the calculated yaw angle command value Ψ_(r).

The pitch angle command value calculating portion 22 calculates thepitch angle command value θ_(t) from a value obtained by integrating avalue obtained by multiplying the input command value of the upper-lowercontrolling force by a gain, and updates the pitch angle command valueθ_(t) as the target value to the calculated pitch angle command valueθ_(r). As above, the yaw angle command value calculating portion 21determines an azimuth of the yaw angle as a target from a value obtainedby integrating the command value of the left-right controlling force.Further, the pitch angle command value calculating portion 22 determinesan azimuth of the pitch angle as a target from a value obtained byintegrating the command value of the upper-lower controlling force.

The yaw angle command value Ψ_(t) as the updated target value iscompared by the second comparing portion 5 c with the actual yaw anglecommand value Ψ measured by the gyro sensor 8, and the differencetherebetween is input to the controlling force calculating portion 6.Further, the updated pitch angle command value θ_(r) is compared by thesecond comparing portion 5 b with the actual pitch angle command value θmeasured by the gyro sensor 8, and the difference therebetween is inputto the controlling force calculating portion 6.

The controlling force calculating portion 6 calculates the pitch turncontrolling force from the above difference regarding the pitch anglecommand value and also calculates the yaw turn controlling force fromthe above difference regarding the yaw angle command value. Then, thecontrolling force calculating portion 6 inputs the command values of therespective turn controlling forces, calculated from the calculationresult, to the thrust distributing device 7. Based on the input commandvalues of the respective turn controlling forces, the thrustdistributing device 7 calculates the operation amounts of the actuators3 for turning the hull 2 in the pitch direction and the yaw directionand outputs the command values of the calculated operation amounts tothe actuators 3. The update of the target value of the yaw angle commandvalue is performed until the left-right controlling force becomes zero,and the update of the target value of the pitch angle command value isperformed until the upper-lower controlling force becomes zero. Thus,the underwater sailing body 10 of Embodiment 2 can change the posturethereof so as to direct the bow in the direction of the external forcewith the hull 2 held at the predetermined position.

According to the underwater sailing body 10 of Embodiment 2, as with theunderwater sailing body 1 of Embodiment 1, the pitch angle of the hull 2may exceed 90°, and the underwater sailing body 10 may take the abnormalposture. To prevent the underwater sailing body 10 from taking theabnormal posture, the underwater sailing body 10 may be configured asbelow.

To be specific, according to the underwater sailing body 10, when theexternal force is applied to the hull 2, first, the pitch angle commandvalue calculating portion 22 sets the value of the gain, by which thecommand value of the upper-lower controlling force is multiplied, tozero, and the turn is performed only in the yaw direction. After theturn in the yaw direction, the yaw angle command value calculatingportion 21 sets the value of the gain, by which the command value of theleft-right controlling force is multiplied, to zero, and the pitch anglecommand value calculating portion 22 returns the value of the gain,which is zero, to the initial value. Then, the turn is performed in thepitch direction.

Or, to prevent the hull 2 from taking the abnormal posture, theunderwater sailing body 10 may be configured such that the speed ofupdating the target value of the pitch angle is lower than the speed ofupdating the target value of the yaw angle. Specifically, in theunderwater sailing body 10, the value of the gain by which the pitchangle command value calculating portion 22 multiplies the command valueof the upper-lower controlling force is set to be smaller than the valueof the gain by which the yaw angle command value calculating portion 21multiplies the command value of the left-right controlling force.

As above, the underwater sailing body 10 according to Embodiment 2 isconfigured such that the turn of the hull 2 in the yaw direction isperformed preferentially over the turn of the hull 2 in the pitchdirection. Therefore, the hull 2 can be prevented from taking theabnormal posture, and the unstable control before and after the abnormalposture can be avoided.

Modified Example

Each of the underwater sailing body 1 of Embodiment 1 and the underwatersailing body 10 of Embodiment 2 is configured to control a rotationaldirection of pitching of the hull 2 by operating a plurality of verticalthrusters 32. However, as shown in FIG. 8, the underwater sailing bodymay be configured such that: a gravity center position changing portion30 configured to be movable in the front-rear direction is included asthe actuator 3; and the inclination of the hull 2 in the upper-lowerdirection, i.e., the rotational direction of the pitching of the hull 2is controlled by changing the gravity center position of the hull 2.FIG. 8 is a diagram schematically showing one example of theconfiguration of a modified example of the underwater sailing body 1,10. FIG. 8 schematically shows the structure of a cross section of theunderwater sailing body 1, 10, the cross section being taken verticallyin the front-rear direction.

The gravity center position changing portion 30 may be a weight made ofmetal, such as lead, or may be an air tank. To be specific, the gravitycenter position changing portion 30 is only required to be able tochange the gravity center position of the underwater sailing body 1, 10in the front-rear direction by moving in the hull 2 in the front-reardirection. As above, when the underwater sailing body 1, 10 includes thegravity center position changing portion 30, the rotational direction ofthe pitching of the hull 2 can be determined by the movement of thegravity center position changing portion 30, and therefore, the controlof the turn in the pitch direction by the vertical thrusters 32 can befacilitated.

From the foregoing explanation, many modifications and other embodimentsof the present invention are obvious to one skilled in the art.Therefore, the foregoing explanation should be interpreted only as anexample and is provided for the purpose of teaching the best mode forcarrying out the present invention to one skilled in the art. Thestructures and/or functional details may be substantially modifiedwithin the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is useful for underwater sailing bodies, such asAUVs, each of which needs to perform work while holding a hull at atarget position in water or needs to hold a hull at a target positionbefore performing work.

REFERENCE SIGNS LIST

-   -   1 underwater sailing body    -   2 hull    -   3 actuator    -   4 first comparing portion    -   4 a first comparing portion    -   4 b first comparing portion    -   4 c first comparing portion    -   5 second comparing portion    -   5 a second comparing portion    -   5 b second comparing portion    -   5 c second comparing portion    -   6 controlling force calculating portion    -   7 thrust distributing device    -   8 gyro sensor    -   9 positioning device    -   10 underwater sailing body    -   11 flow direction meter    -   12 first change rate limiter    -   13 second change rate limiter    -   21 yaw angle command value calculating portion    -   22 pitch angle command value calculating portion    -   30 gravity center position changing portion    -   50 controller

The invention claimed is:
 1. An underwater sailing body comprising: a positioning device configured to detect positional information indicating a position of a hull of the underwater sailing body; a posture detecting sensor configured to detect posture information indicating a posture of the hull; an actuator configured to apply thrust to the hull in a front-rear direction of the hull, a left-right direction of the hull, and an upper-lower direction of the hull in water to change the position and posture of the hull; and a controller configured to control the actuator, wherein: in order to hold the hull at a target position based on the positional information detected by the positioning device, the controller calculates a controlling force in the front-rear direction of the hull, a controlling force in the left-right direction of the hull, a controlling force in the upper-lower direction of the hull, a turn controlling force of turning the hull in a roll direction of the hull, a turn controlling force of turning the hull in a yaw direction of the hull, and a turn controlling force of turning the hull in a pitch direction of the hull, and controls the actuator based on the calculated forces, when an external force is applied to the hull held at the target position, the controller updates target posture information such that each of the controlling force in the left-right direction and the controlling force in the upper-lower direction becomes zero, and controls the actuator such that the posture of the hull is changed to a posture corresponding to the updated posture information based on the posture information detected by the posture detecting sensor, the controller includes a controlling force calculating portion configured to calculate the controlling force in the front-rear direction, the controlling force in the left-right direction, the controlling force in the upper-lower direction, the turn controlling force in the roll direction, the turn controlling force in the yaw direction, and the turn controlling force in the pitch direction from a difference between target positional information and the positional information detected by the positioning device and a difference between the target posture information and the posture information detected by the posture detecting sensor, when the external force is applied to the hull held at the target position, the controller updates a command value of a yaw angle of the target posture information and a command value of a pitch angle of the target posture information such that each of the controlling force in the left-right direction and the controlling force in the upper-lower direction, which are calculated by the controlling force calculating portion, becomes zero, the controller includes: a yaw angle command value calculating portion configured to integrate a value of the controlling force in the left-right direction to calculate a target command value of the yaw angle; and a pitch angle command value calculating portion configured to integrate a value of the controlling force in the upper-lower direction to calculate a target command value of the pitch angle, until each of the controlling force in the left-right direction and the controlling force in the upper-lower direction becomes zero, the controller updates the command value of the yaw angle and the command value of the pitch angle by the command value calculated by the yaw angle command value calculating portion and the command value calculated by the pitch angle command value calculating portion, the yaw angle command value calculating portion calculates the target command value of the yaw angle from a value obtained by integrating a value obtained by multiplying the value of the controlling force in the left-right direction by a gain, the pitch angle command value calculating portion calculates the target command value of the pitch angle from a value obtained by integrating a value obtained by multiplying the value of the controlling force in the upper-lower direction by a gain, and the controller changes a value of the gain by which the yaw angle command value calculating portion multiplies the value of the controlling force in the left-right direction and a value of the gain by which the pitch angle command value calculating portion multiplies the value of the controlling force in the upper-lower direction, and updates the command value of the yaw angle and the command value of the pitch angle in this order, or the controller sets a speed of updating the command value of the pitch angle to be lower than a speed of updating the command value of the yaw angle.
 2. The underwater sailing body according to claim 1, wherein the actuator includes a gravity center position changing portion configured to move in the front-rear direction in the hull so as to change a gravity center position of the hull.
 3. A method of controlling a posture of an underwater sailing body, the underwater sailing body comprising: a positioning device configured to detect positional information indicating a position of a hull of the underwater sailing body; a posture detecting sensor configured to detect posture information indicating a posture of the hull; an actuator configured to apply thrust to the hull in a front-rear direction of the hull, a left-right direction of the hull, and an upper-lower direction of the hull in water to change the position and posture of the hull; and a controller configured to control the actuator, the method comprising: in order to hold the hull at a target position based on the positional information detected by the positioning device, calculating by the controller a controlling force in the front-rear direction of the hull, a controlling force in the left-right direction of the hull, a controlling force in the upper-lower direction of the hull, a turn controlling force of turning the hull in a roll direction of the hull, a turn controlling force of turning the hull in a yaw direction of the hull, and a turn controlling force of turning the hull in a pitch direction of the hull, and controlling the actuator by the controller based on the calculated and forces; when an external force is applied to the hull held at the target position, updating, by the controller, target posture information such that each of the controlling force in the left-right direction and the controlling force in the upper-lower direction becomes zero, and controlling the actuator by the controller such that the posture of the hull is changed to a posture corresponding to the updated posture information based on the posture information detected by the posture detecting sensor; calculating the controlling force in the front-rear direction, the controlling force in the left-right direction, the controlling force in the upper-lower direction, the turn controlling force in the roll direction, the turn controlling force in the yaw direction, and the turn controlling force in the pitch direction from a difference between target positional information and the positional information detected by the positioning device and a difference between the target posture information and the posture information detected by the posture detecting sensor; when the external force is applied to the hull held at the target position, updating, by the controller, a command value of a yaw angle of the target posture information and a command value of a pitch angle of the target posture information such that each of the controlling force in the left-right direction and the controlling force in the upper-lower direction, which are calculated by the step of calculating the controlling forces, becomes zero; integrating a value of the controlling force in the left-right direction to calculate a target command value of the yaw angle; integrating a value of the controlling force in the upper-lower direction to calculate a target command value of the pitch angle; and until each of the controlling force in the left-right direction and the controlling force in the upper-lower direction becomes zero, updating, by the controller, the command value of the yaw angle and the command value of the pitch angle by the command value calculated by the step of calculating the target command value of the yaw angle and the command value calculated by the step of calculating the target command value of the pitch angle, wherein the target command value of the yaw angle is calculated from a value obtained by integrating a value obtained by multiplying the value of the controlling force in the left-right direction by a gain, wherein the target command value of the pitch angle is calculated from a value obtained by integrating a value obtained by multiplying the value of the controlling force in the upper-lower direction by a gain, and wherein the method further includes changing a value of the gain by which the value of the controlling force in the left-right direction is multiplied and a value of the gain by which the value of the controlling force in the upper-lower direction is multiplied, and updating the command value of the yaw angle and the command value of the pitch angle in this order, or setting a speed of updating the command value of the pitch angle to be lower than a speed of updating the command value of the yaw angle. 